Anomalous atomic hydrogen shock pattern in a supersonic plasma jet

A two-photon laser-induced fluorescence study on the transport of ground-st ate atomic hydrogen in a supersonic plasma jet, generated from an Ar-H-2 mi xture, reveals an unexpected shock pattern. Whereas both the axial-velocity profile and the temperature profile of hydrogen atoms along the jet center line can be interpreted in terms of a supersonic expansion of an Ar-H gas m ixture, the H-atom density profiles do not satisfy the well established Ran kine-Hugoniot relation leading to a nc,nonconservation of the forward flux. The experimental results show that H atoms escape from the supersonic expa nsion by a diffusion process due to strong density gradients: between the c ore of the jet and its vicinity.